Add `compute` app function for running compute shaders #764

Job	Run time
nix-fmt-check	23s
nix-flake-check (ubuntu-latest)	28s
nix-flake-check (macos-latest)	1m 5s
cargo (cargo fmt --verbose --all -- --check)	1m 12s
cargo (cargo check --locked --workspace)	4m 26s
cargo (cargo check --locked --examples --workspace)	4m 56s
cargo (cargo test --locked --lib --bins --workspace --features "egui")	10m 11s
cargo (cargo doc --locked --workspace --features "egui")	8m 52s
cargo (cargo test --locked -p nannou_core --no-default-features --features "libm serde")	1m 20s
cargo (mdbook build guide/)	1m 18s
cargo (cargo test --locked -p book_tests)	7m 26s
verifications	1s
guide-push-to-deploy	0s
cargo-publish	0s
	41m 38s

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